1. Field of the Invention
The present invention relates to improving natural lighting within buildings and more particularly to daylight harvesting for building interior illumination. More particularly, this invention relates to daylighting elements of a building such as glazed wall openings, wall windows, roof windows and skylights, as well as to various devices and glazing structures used for admitting and distributing daylight into the interior of a building, such as light shelves, light redirecting blinds or louvers, light diffusers, and optically transmissive plates and light guides employing total internal reflection surfaces.
2. Description of Background Art
Various optical structures for redistributing daylight into building interiors are known. At least some of such prior art devices employ planar transparent plates of glass or plastic materials which include reflective surfaces embedded between the opposing sheet surfaces and configured to reflect light by means of a total internal reflection (TIR). The use of TIR structures generally allows for much larger bend angles compared to refractive structures such as prismatic sheets or films. Large bend angles are particularly important for redistributing daylight in the interior of a building so that at least a portion of the incident daylight could be directed towards the upper portions of the interior, such as the ceiling of a room.
For example, one such light redirecting structure employing internal TIR surfaces is disclosed in U.S. Pat. No. 737,979 which shows a glass plate including a series of parallel slots made in its body. The angle of these slots is such that daylight coming from any given principal direction from outside is reflected from the surface of the slot and is hereby redirected from its original propagation path. Another light redirecting structure is disclosed in U.S. Pat. No. 6,424,406 which describes optical diffuser plates made from transparent plastics and employing either thin strips of another plastic or hollows in the respective plates to deflect light.
U.S. Pat. No. 7,416,315 discloses a faceted reflector which includes a plurality of parallel prismatic reflectors embedded in a carrier and reflecting light by total reflection at a part of the cavity interfaces. In U.S. Pat. No. 6,616,285, total reflection surfaces are formed by merging two optical bodies each having surface groves which interpenetrate into one another when such bodies are placed face-to face. U.S. Pat. No. 5,880,886 shows V-section grooves formed in a major face of a substantially flat and planar optical element. U.S. Pat. No. 4,557,565 discloses a planar solid transparent light deflecting panel or plate for transmitting sunlight into the interior of a building. The panel or plate is formed of a plurality of parallel identically spaced apart triangular ribs on one face. The ribs have specially selected slopes to totally internally reflect light when such panel or plate is placed over an opening such as window.
On the other hand, various methods of making the light redirecting TIR structures in such transparent plates have been proposed. For example, U.S. Pat. No. 4,989,952 discloses a method for producing a transparent light deflecting panel comprising making a series of parallel cuts in a sheet of transparent solid material with a laser cutting tool. Such panel can be positioned in an opening in the facade of a building to deflect incident daylight towards the ceiling thereby improving the natural lighting within the building. The transparent sheet is commonly acrylic and the laser tool is a carbon dioxide (CO2) laser.
U.S. Pat. No. 6,580,559 describes a method of forming internal TIR structures in transparent panels made from glass-like thermoplastic material such as PMMA by inducing parallel crazes in the thermoplastic material. An organic solvent is applied on the panel surface while a tensile stress is applied to a panel which results in generation of wedge-shaped deformations (crazes) which propagate within the material. However, such method of forming internal TIR structures offers little control over the spacing, depth and extent of the crazes, as well as can substantially compromise the structural integrity or rigidity of the panel.
However, the use of prior art light redirecting devices for daylighting purposes can be deficient in that such devices only provide light redirection in one angular dimension, whereas the significant seasonal and hourly positional changes of the sun are two-dimensional (i.e., changes in the elevation and azimuth angle). Thus, many daylighting systems would benefit from employing a sheet-form light redirecting structure that can provide large bend angles in more than one angular dimensions and thus provide a more uniform and broad distribution of daylight in the building interior. On the other hand, such daylighting systems will also benefit from providing additional means for light diffusion which would even further improve light distribution and reduce apparent glare.
These needs and others are met within the present invention, which provides an improved sheet-form structure for illuminating building interiors with sunlight and also provides a method of making the same. The improved sheet-form structure employs internal reflective surfaces disposed in an arrangement which is more efficient for redirecting and distributing sunlight incident from a broad range of directions.